Purpose <p>Fisheries represent a globally significant commercial sector whilst rising demand for fish products has intensified environmental emissions. Despite increasing fish consumption, fisheries have stagnated over the past three decades due to their reliance on wild fish stocks, limiting the potential for increased production. In Life Cycle Assessment, these constraints are often overlooked, not capturing the complexities unique to wild-capture fisheries. The present study addresses this gap by structuring a framework, directly applied to Danish fisheries, designed to advance consequential life cycle assessment for analysing fish consumption.</p> Methods <p>In this study, we investigate supply constraints and marginal markets for various fish species. Our methodological approach employs quantitative data from fish landings and quotas in Denmark to identify supply constraints and qualitative insights from interviews with producer organizations directly involved in the production system. This collaborative approach strengthens the analysis by incorporating the practical knowledge of those working within the sector. Evidence from existing literature is also used to understand substitution choices. This comprehensive approach enables us to address constraints on fish supply and substitution patterns between fish products and alternative food choices.</p> Results and discussion <p>A decision tree is designed to guide the identification of constraints to fish production and supply options, choosing between increasing wild-caught fish production or shifting consumer demand to alternative products. The framework integrates this decision tree and analytical methods. Primary constraints include quota system due to natural resource availability, profitability, and fleet capacity. Findings reveal limited potential for increased Danish landings, highlighting substitution possibilities. Key substitutions include aquaculture species within the same markets or, to a lesser degree, shifting toward land-based alternatives.</p> Conclusions <p>This study addresses critical gaps in the consequential LCA of fish products, namely, the identification of marginal suppliers, by providing a framework to assess supply constraints and describe potential substitutions in response to increased demand. The framework, specific to consequential LCA of fisheries, is proposed as a step-by-step guide outlining the types of data required, such as quota allocations, landings, trade flows, and stakeholder insights, to model fish products more accurately. It supports a data-driven and region-specific approach that improves the applicability of consequential LCA in fisheries.</p>